A direct result of the increased horsepower of modern automotives engines is the proportional increase in the heat generated by these engines. The heat generated by internal combustion engines tends to degrade many of the components of the engine. The high heat at which these engines run also tends to increase emissions, especially of nitrogen oxide. The Environmental Protection agency and the Corporate Average Fuel Efficiency (“CAFE”) standards adopted by the Department of Transportation has identified the reduction of nitrogen oxide as one of their goals. In order to address the CAFE standards and the negative impact of the increased heat generation in today's high horsepower engines, automotive manufacturers have had to resort to increasingly complex cooling systems for these engines. The complexity of these cooling systems has increased not only the expense of manufacturing these engines, but also their weight and the potential for flaws in the cooling system—both during manufacture and while in use.
Three components or regions of the internal combustion engine where heat is concentrated are the combustion chambers, cylinder bores, and pistons. To cool these regions or components, internal combustion engines are designed with numerous passages through which fluids—oil, water, coolants, or gases (e.g., air)—are circulated to draw heat away from the engine block. Furthermore, engine designs incorporate cylinder liners to avoid degradation of the cylinder bores caused by heating and cooling. A cylinder liner, typically made of ductile iron, is a hollow cylinder whose outside diameter is close to the internal diameter of the cylinder bore, so that the liner fits inside the cylinder bore snugly. The piston travels inside the cylinder liner, thus heating up the cylinder liner first instead of directly transferring its heat to the cylinder bore and the engine block itself. The use of cylinder liners helps alleviate degradation of the cylinder bore due to the heat, but in turn creates problems related to degradation of the cylinder liners due to excessive heating. Thus, cylinder liners are a fourth component of internal combustion engines that are subject to degradation and failure due to excessive heating. Because cylinder liners are such an integral part of the design of internal combustion engines and because they play such a crucial role in avoiding degradation of the engine block itself, various techniques have been developed expressly to address the cooling of cylinder liners in today's high horsepower engines.
Cylinder liners can be either of the dry-sleeve or wet-sleeve design. In a wet-sleeve design, a cooling medium is present between at least part of the interior surface of the cylinder bore and the outer surface of the liner. The engine block is designed with a complex series of passages for this cooling medium to be brought in contact with the liner and then removed to a heat exchange location (e.g., a radiator) where the medium can release the heat it drew from the cylinder liner and cylinder bore. In a dry-sleeve design, the outer surface of the liner and the interior surface of the cylinder bore are for the most part in direct contact. Although there is no fluid present between the interior surface of the cylinder bore and the outer surface of the cylinder liner, fluids are still circulated within the engine block, through a complex series of passages, to draw heat away from the cylinder bore and the cylinder liner. The complexity of the layout of the passages and process of circulating the cooling medium uniformly round all of the cylinder bores is especially accentuated in engines where the cylinder bores are arranged in a “V”-formation (e.g., V-8s and V-12s) because these engines tend to have reservoirs for the cooling medium arranged on one-side of the engine; necessitating a complex series of passages to circulate fluids to the other side.
In some engines, oil is squirted through a small tube or plurality of tubes into the bottom of the cylinder bore and allowed to hit the bottom of the piston. The oil that is squirted in, using these “oil squirters” or “piston squirters,” cools down the piston and increases lubrication. Piston squirters are not incorporated as part of the system of passages that carry the cooling medium but instead are incorporated as separate systems dedicated only to transporting oil from the oil-pan to the bottom of the cylinder bore.
In addition to the increased cost of engine block design and manufacture necessitated by the current dry-sleeve or wet-sleeve design, a primary shortcoming of the wet-sleeve design is the non-uniform distribution of the cooling fluid surrounding the cylinder liner. The non-uniform distribution leads to uneven cooling of the liner, the development of hot spots, and the eventual cracking or failure of the liner. Prior art wet-sleeve designs have attempted to address this problem by changing the shape and structure of the outer surface of the cylinder liner (e.g., U.S. Pat. No. 6,675,750 to Wagner). However, while this design increases the surface area of the liner that is exposed to the cooling medium, it fails to address the problem of non-uniform distribution of the cooling fluid because the fluid is not in contact with the entire axial length of the liner.
This design also does not reduce the requirement for a complex series of passages within the engine block for circulating the cooling medium to and from the area between the cylinder bore and the cylinder liner. Furthermore, the design increases the complexity and manufacturing cost of producing cylinder liners by changing the typically planar outer surface of the liner to “an outer surface with a plurality of peaks and valleys” (see U.S. Pat. No. 6,675,750 patent, at col. 2, 11, 15-16).
Additionally, while the above-described designs and approaches are directed at cooling the cylinder areas, they do not address the problem presented by engine ‘cold-start’ and idle periods; during which times substantial excessive pollution/emissions are generated because the cylinders are not at an appropriate temperature to provide for optimally efficient combustion. This is a serious problem in the trucking industry, and has led to increasingly more stringent regulations regarding idling periods. Therefore, the above-described prior art efforts to improve cooling of cylinder liners actually create additional problems from the standpoint of pollutants being generated during cold-starting and idling.
There is, therefore, a pronounced need in the art for cylinder liners that are cost effective and easy to manufacture, allow uniform distribution of cooling fluids along their axial length, and facilitate the design of simpler engine blocks with less complicated passages for circulating cooling fluids. There is also a pronounced need in the art for piston squirters integrated into the circulation system for cooling the cylinder liner and cylinder bore, to preclude the need for an entirely separate squirter circulation system. Moreover, there is a pronounced need for cylinder liners that allow for different cooling fluids (e.g., oil and water, or oil and ethylene-glycol, or water and a compressed inert gas such as nitrogen) to be independently circulated through the liner. Where oil is used as the liner cooling medium, there is also a need for cylinder liners that allow for the oil to circulate within a closed loop, thus avoiding directing oil on to the crankshaft. Oil directed (e.g., dripped) on the crankshaft leads to increased emissions and peristaltic drag, thus a design that eliminates direction of oil onto the crankshaft decreases emissions as well as peristaltic drag. Furthermore, there is a pronounced need in the art for cylinder liners with enhanced thermal conductivity to improve heat transfer/dissipation. Finally, there is a pronounced need in the art for cylinder liners that have enhanced electrical conductivity to allow for thermoelectric heating of the cylinder liners during engine warm-up, particularly in larger engines such as, but not limited to diesel engines of, for example, trucks and the like. There is a need to shorten warm-up periods and reduce pollution, while still providing for cooling and enhanced engine life.